Charge variation may occur between battery cells of a battery pack. The charge variation may be related to battery cell manufacturing tolerances, environmental differences within the battery pack, or other factors. Imbalance between battery cells may not be desirable because imbalance may lead to reduced battery capacity utilization. One way to increase battery capacity is to balance charge between battery cells. By balancing or equalizing charge between battery cells, it may be possible for the battery pack to reach a higher charge capacity since all battery cells may be brought to a desired level of charge. For example, charge can be drained from battery cells that achieve an upper voltage limit before other battery cells reach the upper voltage limit. By draining charge from lower capacity battery cells (e.g., battery cells that are first to reach a voltage limit during charging) during batter charging, it is possible to increase charge of higher capacity battery cells (e.g., battery cells that reach a voltage limit later during charging). However, even though the battery pack may be brought to a higher level of charge, the instantaneous amount of current supplied to lower capacity battery cells may be higher than is desired. Consequently, battery cell charging components may have to be sized with a higher current capacity than is desired.
The inventors herein have recognized that it is desirable to control current within the battery pack so that battery pack components may operate at lower current levels. Accordingly, the inventors herein have developed a method for actively balancing charge of a battery pack, comprising: discharging a plurality of battery cells via a first current path during a second battery discharge cycle; providing charge to a first battery cell via a first flyback transformer during said second battery discharge cycle, said flyback transformer in a second current path; providing charge to a second battery cell via a second flyback transformer during said second battery discharge cycle, said second flyback transformer in said second current path, said charge provided to said second battery cell by providing charge to said second flyback transformer at a different timing than charge provided to said first flyback transformer.
By actively balancing charge between battery cells and by controlling the timing of battery cell charging, it may be possible to increase the usable capacity of a battery pack while limiting current flow within the battery. In particular, less instantaneous current may be supplied to battery cells when charge is supplied to different battery cells at different times. For example, rather than charging a first and second battery cell at the same time, the first battery cell can be charged at a first time while the second battery cell is charged at a second time, the first time different than the second time. Since the charging current is supplied at different times, less peak current capacity may be required of a power supply that supplies charge to battery cells.
The present description may provide several advantages. In particular, the method may reduce peak current demand within a second charging path of a battery pack. In addition, the present method may reduce electrical noise and lower voltage ripple.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.